Compression heat pump, in particular for applications near households

ABSTRACT

A system for household-related heat recovery from waste water includes a compression heat pump having a compressor for a coolant, a condenser, and an evaporator. Disposed between the condenser and the evaporator is an expansion valve, and a temperature probe is arranged on the evaporator at a location at which coolant is injected. A switching valve switches over a flow resistance of the expansion valve between two fixed flow resistance values. Below a predetermined temperature at the temperature sensor, the switching valve switches over to low flow resistance of the expansion valve and above the predetermined temperature, the switching device switches to a higher flow resistance of the expansion valve.

The invention relates to a compression heat pump, in particular for household-related applications such as heat recovery from waste water, for refrigerating or air conditioning apparatus and the like, with a compressor for a coolant, a condenser, an evaporator and also an expansion valve disposed between condenser and evaporator.

In order to achieve an optimum mode of operation of such compression heat pumps—especially with varying thermal loads—it is necessary to regulate the evaporation pressure or the evaporation temperature respectively. If the evaporation pressure is namely too low, the efficiency is unfavorable, while with evaporation pressure that is too high the compressor is subjected to unnecessarily high loads and thus under some circumstances is loaded impermissibly, which can lead to its premature failure.

With large refrigeration systems and heat pumps, especially with connected loads that are greater than 500 W, it is therefore usual to regulate the evaporation pressure or the evaporation temperature respectively by a variable expansion valve. This regulation can either be undertaken directly via the evaporation pressure by means of pressure-controlled valves, which do not require any electronics. Likewise the temperature at the evaporator can also serve as a regulation variable, wherein a setting signal for the expansion valve is then created by means of control electronics from the deviation of the current temperature from the setpoint temperature. The expansion valve itself can in such cases be controlled both electrically and also pneumatically.

With small refrigeration systems on the other hand, for reasons of cost, a non-variable expansion valve is generally employed, which can consist of a capillary tube for example. This does not enable an optimal level of efficiency to be achieved under the variable conditions discussed above.

The underlying object of the invention is thus to improve a compression heat pump of the type described at the start such that an almost constant evaporation temperature can be set in a cost-effective manner, so that on one hand a good level of efficiency and on the other hand a long service life, especially of the compressor, can be achieved.

A compression heat pump achieving this object is characterized by a switching valve for switching over the flow resistance of the expansion valve between two fixed flow resistance values and also by a temperature probe in the region of the injection point of the coolant at the evaporator, wherein the switching valve, below a predetermined temperature at the temperature probe, is switched over to a lower flow resistance and above this temperature is switched over to a higher flow resistance of the expansion valve.

The advantage obtained by the invention essentially lies in the fact that, with only slight extra outlay compared to a non-variable throttle, a marked increase in the efficiency can be achieved, even with a small heat pump. In particular the invention allows the space occupied by such a device to be reduced compared to a variable expansion valve. The simple switchover between two different flow resistances also enables commercially-available and thereby low-cost refrigeration components to be used.

In a preferred embodiment of the invention the expansion valve is formed by two throttles with a fixed flow resistance, which are selected via the switching valve.

Individually this results in different design options; the preferred option is an embodiment in which the switching valve is embodied as a switchover valve and switches between two throttles with different flow resistance.

However it is also possible for the two throttles to be switched in parallel with one another, wherein the switching valve is embodied as a closing valve and is disposed in the flow branch of the one throttle. In this mode of operation the one throttle always has coolant flowing through it, if necessary the second throttle is also switched in parallel by the switching valve, through which the flow resistance is reduced.

However there is also the option here of connecting the two throttles behind one another, wherein the switching valve is embodied as a closing valve and is disposed as a bypass in parallel to one of the two throttles. If the switching valve is closed here, both throttles are active, which produces a higher flow resistance than with an opened closing valve short-circuiting the one of the two throttles.

Control electronics is provided as well for detection and evaluation of the temperature and for actuation of the switching valve. This electronic control thus also allows the adaptation of the setpoint evaporation temperature to other operating parameters; thus for example the evaporation temperature can be adapted as a function of the temperature in the evaporator.

The invention is explained in greater detail below by an exemplary embodiment shown in the drawing, in which:

FIG. 1 shows the dependence of the evaporation temperature on the operating time of the heat pump,

FIG. 2 shows a diagram corresponding to FIG. 1, but with a mode of operation in accordance with the invention,

FIG. 3 shows a schematic diagram of the inventive layout.

The compression heat pump shown in the drawing in FIG. 3 is intended especially for household-related applications, i.e. for example for heat recovery from waste water, for refrigerating or air conditioning apparatus and the like.

This compression heat pump consists—as is usual—first of all of a compressor 1 for a coolant to be pumped around within the coolant circuit, also of a condenser 2 emitting heat, also of an evaporator 3 taking up heat, as well as an expansion valve 4 disposed between condenser 2 and evaporator 3.

With small refrigeration systems such as household refrigerating apparatus or compact air conditioning apparatus, a non-variable throttle organ is mostly employed as the expansion valve 4 for reasons of cost, which for example can be formed by a capillary tube. As a result of the varying thermal loads acting on such a heat pump however the evaporation pressure or the associated evaporation temperature varies during operation. This is shown by way of example in FIG. 1, where initially the evaporation temperature lies comparatively low then however increases during a further period of operation and finally reaches the optimal evaporation temperature for an efficient operation. In continuing operation however the evaporation temperature increases further, which leads to an increased load on the compressor 1.

With large refrigeration systems it is thus usual to regulate the evaporation pressure or the evaporation temperature via a variable expansion valve 4, but this is something which is not done with small systems, in view of the effort and the expense involved.

As part of the invention a two-point regulation by a switching valve 5 is thus proposed, that serves to switch the flow resistance of the expansion valve 4 between two fixed flow resistance values. Furthermore a temperature probe not presented in any greater detail is provided in the region of the injection point of the coolant at the evaporator, with the aid of which the switching valve 5, below a predetermined temperature at the temperature probe, switches over to the lower flow resistance and above this temperature switches over to the higher flow resistance of the expansion valve 4. Viewed over the service life of the valve, this enables a temperature curve to be achieved as is shown in FIG. 2.

In detail the expansion valve 4 is formed in a manner not shown in any greater detail by two throttles with a fixed flow resistance, which are selected via the switching valve 5. In this case the switching valve is embodied as a switchover valve and switches between two throttles with different flow resistance. In this embodiment the one of the two throttles determines the higher flow resistance and the other of the two throttles the lower flow resistance.

However the option also exists of switching both throttles in parallel to one another, wherein the switching valve is embodied as a closing valve and is disposed in the flow branch of the one throttle. The lower flow resistance is then achieved here when coolant flows through both throttles.

In a corresponding manner the two throttles can also be connected one behind the other, wherein the switching valve 5 is likewise embodied as a closing valve and is disposed as a bypass in parallel to one of the two throttles.

To detect and evaluate the temperature, control electronics not shown in any greater detail in the figure is provided, which additionally also allows further operating parameters, i.e. for example the adaptation of the evaporation temperature as a function of the temperature in the evaporator.

Thus, even with heat pumps for small refrigerating apparatus, efficient operation largely independent of the load conditions is possible, without expensive, variable expansion valves having to be employed for this purpose. 

1-6. (canceled)
 7. A system for household-related heat recovery from waste water, comprising: a compression heat pump having a compressor for a coolant; a condenser; an evaporator, and an expansion valve disposed between the condenser and the evaporator; a temperature probe arranged on the evaporator at a location at which coolant is injected; and a switching valve for switching over a flow resistance of the expansion valve between two fixed flow resistance values, said switching valve switching over to a first flow resistance below a predetermined temperature at the temperature probe and switching over to a second flow resistance of the expansion valve above the predetermined temperature, said second flow resistance being higher than the first flow resistance.
 8. The system of claim 7, wherein the expansion valve is formed by two throttles with fixed flow resistance that are selected via the switching valve.
 9. The system of claim 8, wherein the switching valve is embodied as a switchover valve and switches between the two throttles with different flow resistance.
 10. The system of claim 8, wherein the two throttles are connected in parallel to one another, said switching valve being embodied as a closing valve and disposed in a flow branch of one of the two throttles.
 11. The system of claim 8, wherein the two throttles are connected behind one another, said switching valve being embodied as a closing valve and disposed as bypass in parallel to one of the two throttles.
 12. The system of claim 7, further comprising a control electronics constructed to detect and evaluate a temperature and to actuate the switching valve. 